1. Field of the Invention:
The present invention relates, in general, to emission-related diagnostics and/or control algorithms in a power train control module and, specifically, to the diagnosis of malfunctions of the Ignition-Off Timer.
2. Description of the Art:
Ignition-off time is the amount of time measured from the point where an xe2x80x9coffxe2x80x9d condition of the ignition of an internal combustion engine is detected to the point where an xe2x80x9conxe2x80x9d condition is detected, called an ignition-off event. The Ignition-Off Timer function measures, saves and reports the timed duration of the last ignition-off event to the engine controller. The Timer begins functioning when an xe2x80x9coffxe2x80x9d condition is detected. It resets to zero or one second (depending upon the implementation) and starts incrementing until an xe2x80x9conxe2x80x9d condition is encountered. Any ignition-off time of less than or equal to one second is reported to the engine controller as one second. If ignition-off time exceeds a specified maximum duration, usually seven days, the Ignition-Off Timer reports the maximum value in the range to the engine controller.
Among other uses, ignition-off time is used by emission-related diagnostics and/or control algorithms. Therefore, diagnosis of the Ignition-Off Timer is required by the California Air Resources Board (CARB) On-Board Diagnostic II (OBD II) requirements. In particular, diagnosis is required under section (a) (1.0) of the CARB regulation 1968. 1, which provides that all vehicles xe2x80x9cshall be equipped with a malfunction indicator light (MIL) located on the instrument panel that will automatically inform the vehicle operator in the event of a malfunction of any power train components which can affect emissions and which provide input to or receive output from the on-board computer(s) or of the on-board computer(s) itself.xe2x80x9d In addition to emission-related uses, ignition-off time is becoming increasingly important for other diagnostics and controls, such as fuel control.
Thus, it is desirable to develop a method and apparatus to determine whether the Ignition-Off Timer is working properly. In particular, the Ignition-Off Timer should be monitored while it is functioning to determine if it resets and increments properly, and malfunctions should be reported.
The present invention is a method and apparatus for monitoring the function of an Ignition-Off Timer and reporting the presence of any one of the following failure conditions:
1. Timer is stuck in range;
2. Timer has timing error (counts too slow or too fast);
3. Timer decrements instead of increments;
4. Timer outputs random variables; or
5. Timer exceeds expected range after reset.
The Ignition-Off Timer resets and begins incrementing when the ignition of an internal combustion engine is shut off and continues incrementing until the ignition is turned on. Each time the Timer resets and begins incrementing, the present invention tests the first few seconds of the operation of the Timer. Essentially, the output of the Timer is compared against various reference values, some of which are obtained through the use of another timer, external to the Ignition-Off Timer. Whether the Ignition-Off Timer passes or fails is reported to the diagnostic control manager.
Initialization of the variables used in the diagnostic occurs when the ignition is turned on. After initialization, the engine controller begins sampling the Timer at predetermined intervals.
The Timer does not begin incrementing and is not diagnosed until it is enabled. Therefore, after sampling the Timer, the engine controller queries whether the Timer is enabled. If the Timer is not enabled, the Timer is again sampled. The Timer is then re-checked to see if it is enabled. This control loop continues until the Ignition-Off Timer is enabled, as reported to the engine controller. Once the Timer is enabled, the sampled output time from the Ignition-Off Timer is stored as a base value for ignition-off time, and the diagnostic operation begins.
First, the diagnostic of the present invention checks a flag indicating whether a test is required or not. If the test has already been completed since the ignition was turned off, the Timer will not be tested again, and the diagnostic ends. However, if the test was not completed since the ignition was turned off, the diagnostic proceeds to sample the Timer.
The diagnostic next checks whether the sampled ignition-off time is within a predetermined range of expected values. If the sampled time is outside the predetermined range, the Timer has failed the diagnostic. The failure is reported to the diagnostic control manager, and the flag is set indicating that a test of the Timer is no longer required. The diagnostic then ends.
If the sampled time is within its predetermined range, the diagnostic checks whether the Timer has incremented since the last time it was sampled. This is accomplished by comparing the sampled value to the previously stored value of ignition-off time. If the sampled value is less than the stored ignition-off time, the Timer has failed the diagnostic. The failure is reported to the diagnostic control manager, and the flag is set indicating that a test of the Timer is no longer required. The diagnostic then ends.
If the sampled time is equal to the stored ignition-off time, then the Timer has not incremented. The sample counter is incremented by one. Then, the sample counter is compared to a predetermined high limit. If the sample counter is higher than the high limit, then the Timer has failed the diagnostic. The failure is reported to the diagnostic control manager, and the flag is set indicating that a test of the Timer is no longer required. The diagnostic then ends. If, however, the sample counter is less than or equal to its predetermined maximum count, the diagnostic begins again by sampling the Timer, checking if the sampled time is out-of-range, and checking to see if the Timer incremented. This continues until the Timer either fails the diagnostic or increments.
If the sampled time is greater than the stored ignition-off time, the Timer has incremented. The transition counter is incremented by one count to indicate the change in value of the Timer. The value of the transition counter is compared to a threshold value for the transition counter. If the transition counter is not above the threshold value, the sample counter is reset, and the sampled time is stored in place of the previously stored ignition-off time. Then, the diagnostic begins again with sampling the Timer, checking if the sampled time is out-of-range, and checking to see if the Timer incremented. This continues until the Timer fails, or it increments. If the Timer increments, the transition counter is incremented by one count. The transition counter is again compared to the threshold value.
Once the transition counter is greater than the transition threshold, the diagnostic makes two inquiries. First, the diagnostic queries whether the sample counter is within a predetermined acceptable range of values. The second inquiry made is whether the sampled time minus the stored ignition-off time is equal to one increment of the Timer. If the sample counter is outside the predetermined acceptable range of values, or the sampled time minus the stored ignition-off time is not one increment of the Timer, then the Timer has failed the diagnostic. Then, the sample counter is reset. The sampled time is stored in place of the previously stored ignition-off time. The failure is reported to the diagnostic control manager, and the flag is set indicating that a test of the Timer is no longer required. The diagnostic then ends.
If, however, the sample counter is inside its predetermined acceptable range of values, and the sampled time minus the stored ignition-off time is equal to one increment of the Timer, the Timer has passed the diagnostic. This pass is reported to the diagnostic control manager, and the flag is set indicating that a test of the Timer is no longer required. The diagnostic then ends.
The apparatus of the present invention diagnoses the Ignition-Off Timer. The apparatus includes means for sampling the Ignition-Off Timer at the specified sampling intervals, means for comparing the sampled output time to various references, and means for reporting whether the ignition-off timer is malfunctioning or not based on the results of the comparison.
The method and apparatus of the present invention provide a novel approach for diagnosing malfunctions of the Ignition-Off Timer. Prior to the present invention, the Ignition-Off Timer was undiagnosed. In addition to the CARB regulation requiring the diagnosis of the Timer, the increased importance of ignition-off time in the operation of internal combustion engines makes the present invention a desirable addition to the on-board diagnostics of an automobile.